A certain portion of opposed curved sides of a log to be cut into lumber pieces is unusable for lumber. That portion is removed from the log (referred to as opening the face of the log) and cut into chips for pulp. A process for removing and chipping the unusable portions of a log involves first cutting the portions from the log, e.g., using a band saw or circular saw, and then sending the cut off portions through a chipper for reducing the portions to chips. Obviously if the log portion can be chipped from the log directly, one step or operation of the process is eliminated which is highly desirable.
Chippers have been developed for accomplishing open faced chipping, i.e., removing and chipping the unusable portions in one operation. A log is directed through a chipping station and a chipper on each side of the log is manipulated to chip the "unusable" portions and in the process produces opposed flat parallel faces spaced apart at a desired dimension. The logs (now referred to as cants) are then cut into flitches with each flitch having parallel side surfaces of a specific width that are then trimmed into boards.
A criteria of the chippers used for opening the faces of the log is that they need to produce an acceptably smooth surface as that surface will ultimately be one side of a board. If the surface is gouged or feathered, the log or cant will have to go through a secondary finishing operation which defeats the objective of accomplishing the opening of the log and chipping the non-usable portions in one operation.
To achieve the smooth surface, a chipper used for open faced chipping is provided with multiple sets of a pair of cooperating blade edges referred to as a hogging blade edge and a finishing blade edge. The hogging blade edge is angled into the log and determines the depth of cut of a chip (the depth terminating precisely at the face) and the finishing blade cuts off the chip at the desired open face, the finishing cut being co-planar with the face. Each blade set follows one after the other in an overlapping manner and as long as all of the finishing blade edges are cutting in exactly the same plane, a smooth flat face is produced.
The exact setting of multiple blade edges in a common plane is not feasible and an acceptable tolerance for the setting of the finishing blades is about plus or minus 0.002 inches from the established plane of the face. A variation of plus or minus 0.002 inches is acceptable for lumber production as long as the face is perceptively smooth, i.e., it contains no unsightly ridges or feathered wood fibers.
In the open faced chippers currently in use, the finishing blade edge is a flat edge oriented in the plane of the face or parallel to the plane of the face plus or minus 0.002 inches. One blade follows the next blade and because there is some offset, e.g., by several thousandths of an inch, the cuts are not in alignment and accordingly the cuts do not intersect each other. The wood fiber in the gap between the offset cuts is ripped off rather than being cut off. The gap itself produces a ridge or groove and the tearing of the fibers will produce the undesired feathering of the open face, particularly as the cutting edge corners become dulled.
Accordingly, an objective of the present invention is to reduce or eliminate the undesired grooves and feathering produced during open faced chipping.